1. Field of the Invention
The present invention relates to an apparatus and method to produce steam, gas and stable solid waste without wastewater discharge. Carbon or hydrocarbon fuel and low quality water (like non-segregating fine tailings, brine from distillation facility, sludge from water softening process and sewage) can be used in a direct contact heat exchange process.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98.
The main characteristic of a direct contact steam generator is that the produced steam contains impurities, such as combustion products (mainly gases and possible solids) that were burned during steam production. Those gases are mainly carbon dioxide and nitrogen, when air is used for stoichiometric combustion processes. Additional gases can be present in smaller percentages, such as CO, SOX, NOX and other gases.
The need for the present invention is driven by challenges facing the heavy oil production industry involved with enhanced oil recovery (EOR) and is especially driven by the negative environmental effect of that type of oil development. For example, steam assisted gravity drainage (SAGD), cyclic steam stimulation (CSS) and open mining of tar sands generate large amounts of tailing water and CO2 emissions. Indirect steam generators, mainly Once Through Steam Generators (OTSG) and steam boilers, are currently used for commercial projects. In the prior art systems, the facilities generate large amounts of wastewater from the water treatment plants (like evaporator brine, lime softening sludge, filter backwash etc). The blow-down from the steam generation facility, especially if OTSG is used, also generates large amounts of wastewater with high levels of solids. With open mine oil sand facilities, due to the separation process of the tar from the bitumen, large amounts of non-segregate fine tailings are generated. There is also a need to use the extensive heat process to extract pure water from the wastewater while recovering the heat and producing a stackable solid waste that can support traffic. There is also a need to utilize low quality carbon fuels such as coal, coke, and asphaltin as the energy source for steam production in the heavy oil production industry to replace the widespread use of natural gas. Natural gas is a clean and valuable resource that, from a public perspective, should not be used for steam production in heavy oil extraction. This clean resource should be preserved and used for residential purposes. The present invention can work with natural gas or other clean liquid/gas fuels, however, due to its ability to handle the solids, both from the water and the fuel as well as its ability to remove SO2, the use of dirty fuel and low quality water is preferred.
Various patents have been issued that are relevant to the present invention. For example, U.S. Pat. No. 2,916,877, issued on Dec. 15, 1959 to Walter, teaches a pressure fluid generator, which utilizes direct-contact heat transfer. The pressure fluid generator is in the form of an elongated combustion chamber. A coolant in the heat exchange relationship is injected into the combustion chamber to form with the combustion products therein, as a gas and superheated vapor-working mixture at a relatively high temperature and pressure. Some embodiments include in-line soot filters and circulated water, and the fuel is hydrocarbon gas.
U.S. Pat. No. 4,398,604, issued on Aug. 16, 1983 to Krajicek et al. describes a system for aboveground stationary direct contact horizontal steam generation. The method and apparatus produces a high-pressure thermal vaporized stream of water vapor and combustion gases for recovering heavy viscous petroleum from a subterranean formation. High-pressure combustion gases are directed into a partially water-filled vapor generator vessel to produce a high-pressure stream of water vapor and combustion gases. The produced solids are continually removed with reject water.
There are also patents relating to applications in heavy oil production. U.S. Pat. No. 4,463,803, issued to Wyatt on Aug. 7, 1984 describes a system for down-hole stationary direct contact steam generation for enhanced heavy oil production. The method and apparatus generate high-pressure steam within a well bore. The steam vapor generator is constructed for receiving and mixing high-pressure water, fuel and oxidants in a down-hole configuration. The produced solids are discharged to the oil reservoir.
Various patents have disclosed rotational elements of steam generators. U.S. Pat. No. 1,855,819, issued on Apr. 26, 1932 to Blomquist et al. describes a rotary boiler, where the pressure chamber is rotating inside the combustion area while producing the steam in an adjacent indirect heat exchanger. To increase the efficiency of the invention, Blomquist used scraper chains within the steam generating tubes, to prevent the sludge from adhering to the tubes interior walls. British patent No. 0 328 339, issued on May 1, 1930 to Kalabin teaches a direct contact steam generator with a rotating pressure vessel. The gasses flow to a rotating chamber, where they are mixed with air and combusted completely. Water covers the walls of the rotating chamber. This is achieved by the centrifugal force of the rotating chamber, exposing the water to gas combustion.
Various patents have disclosed rotating drums with chains as heat exchange elements. These are designed to capture heat from the combustion gas and transfer it to the liquid or slurry medium. U.S. Pat. No. 1,313,281, issued on Aug. 19, 1919 to Fasting describes a rotary kiln for slurry material. The chains lift the slurry onto the path of the hot combustion products, to increase the heat transfer and slurry evaporation. U.S. Pat. No. 4,207,290, issued on Jun. 10, 1980 to Lee, discloses a flue gas scrubber. The elongated tubular drum scrubber, fitted with chains as means of heat transfer, is used for increasing the direct contact between lime slurry and sulfur rich flue gas. The rotating scrubber has two main areas: a scrubbing area with liquid slurry and a drying area. In the drying area, the heat from the flue gas evaporates the moisture to generate dry pellets.
It is an objective of the present invention to provide an apparatus and method for the production of steam and solid waste using a direct contact heat transfer between available low quality water and combustion gases in a rotating or fluid bed reactor.
It is another object of the present invention to provide an apparatus and method where the waste solids are separated and removed in the form of dry particles or high concentrated slurry from the rotating steam generator by rotating apparatus, with a controlled amount of water.
It is another object of the present invention to provide an apparatus and method that produces steam from low-quality tailing pond and reject-water containing high levels of dissolved inorganic solids or organic solids. All liquid water is converted to steam and no liquid is discharged from the apparatus.
It is another object of the present invention to provide an apparatus and method that produces steam from low-quality fuel containing inorganic impurities. For example fuels like coal, coke, asphaltin or any other available carbon based fuel, wherein the combustion byproducts of this fuel are slag and ash in solid form.
It is another objective of the present invention to provide an apparatus where evaporator brine is heated by combustion gas and converted to steam and solids, while the heat to evaporate the brine is under a controlled pressure; the heat is used to operate the evaporator that operates in lower pressure and temperature.
It is a further objective of the present invention to provide an apparatus and method where the concentrate from the crystallizer is heated by combustion energy in direct contact to generate steam and stackable solids and the heat is recovered to operate the crystallizer and possibly the evaporator.
It is an object of the present invention to reduce the need to remove solids from the discharge flow.
It is an object of the present invention to integrating a solids removal step during rotation of a direct contact steam generator.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.